Merge pull request AvaloniaUI#7634 from AvaloniaUI/fixes/7633-date-time-picker-popup

Fix Date/Time picker popups
# Conflicts:
#	src/Avalonia.Controls/DateTimePickers/DatePicker.cs
#	src/Avalonia.Controls/DateTimePickers/TimePicker.cs

Author: maxkatz6

src/Avalonia.Controls/DateTimePickers/DatePicker.cs

@@ -4,6 +4,7 @@
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
 using Avalonia.Interactivity;
+using Avalonia.Layout;
 using System;
 using System.Collections.Generic;
 using System.Globalization;
@@ -398,18 +399,27 @@ private void SetSelectedDateText()
         private void OnFlyoutButtonClicked(object sender, RoutedEventArgs e)
         {
             if (_presenter == null)
-                throw new InvalidOperationException("No DatePickerPresenter found");
+                throw new InvalidOperationException("No DatePickerPresenter found.");
+            if (_popup == null)
+                throw new InvalidOperationException("No Popup found.");
 
             _presenter.Date = SelectedDate ?? DateTimeOffset.Now;
 
+            _popup.PlacementMode = PlacementMode.AnchorAndGravity;
+            _popup.PlacementAnchor = Primitives.PopupPositioning.PopupAnchor.Bottom;
+            _popup.PlacementGravity = Primitives.PopupPositioning.PopupGravity.Bottom;
+            _popup.PlacementConstraintAdjustment = Primitives.PopupPositioning.PopupPositionerConstraintAdjustment.SlideY;
             _popup.IsOpen = true;
 
+            // Overlay popup hosts won't get measured until the next layout pass, but we need the
+            // template to be applied to `_presenter` now. Detect this case and force a layout pass.
+            if (!_presenter.IsMeasureValid)
+                (VisualRoot as ILayoutRoot)?.LayoutManager?.ExecuteInitialLayoutPass();
+
             var deltaY = _presenter.GetOffsetForPopup();
 
             // The extra 5 px I think is related to default popup placement behavior
-            _popup.Host.ConfigurePosition(_popup.PlacementTarget, PlacementMode.AnchorAndGravity, new Point(0, deltaY + 5),
-                Primitives.PopupPositioning.PopupAnchor.Bottom, Primitives.PopupPositioning.PopupGravity.Bottom,
-                 Primitives.PopupPositioning.PopupPositionerConstraintAdjustment.SlideY);
+            _popup.VerticalOffset = deltaY + 5;
         }
 
         protected virtual void OnSelectedDateChanged(object sender, DatePickerSelectedValueChangedEventArgs e)

src/Avalonia.Controls/DateTimePickers/DatePickerPresenter.cs

@@ -534,6 +534,9 @@ private void OnMonthChanged(object sender, EventArgs e)
 
         internal double GetOffsetForPopup()
         {
+            if (_monthSelector is null)
+                return 0;
+
             var acceptDismissButtonHeight = _acceptButton != null ? _acceptButton.Bounds.Height : 41;
             return -(MaxHeight - acceptDismissButtonHeight) / 2 - (_monthSelector.ItemHeight / 2);
         }

src/Avalonia.Controls/DateTimePickers/TimePicker.cs

@@ -3,6 +3,7 @@
 using Avalonia.Controls.Shapes;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
+using Avalonia.Layout;
 using System;
 using System.Globalization;
 
@@ -254,16 +255,28 @@ protected virtual void OnSelectedTimeChanged(TimeSpan? oldTime, TimeSpan? newTim
 
         private void OnFlyoutButtonClicked(object sender, Interactivity.RoutedEventArgs e)
         {
+            if (_presenter == null)
+                throw new InvalidOperationException("No DatePickerPresenter found.");
+            if (_popup == null)
+                throw new InvalidOperationException("No Popup found.");
+
             _presenter.Time = SelectedTime ?? DateTime.Now.TimeOfDay;
 
+            _popup.PlacementMode = PlacementMode.AnchorAndGravity;
+            _popup.PlacementAnchor = Primitives.PopupPositioning.PopupAnchor.Bottom;
+            _popup.PlacementGravity = Primitives.PopupPositioning.PopupGravity.Bottom;
+            _popup.PlacementConstraintAdjustment = Primitives.PopupPositioning.PopupPositionerConstraintAdjustment.SlideY;
             _popup.IsOpen = true;
 
+            // Overlay popup hosts won't get measured until the next layout pass, but we need the
+            // template to be applied to `_presenter` now. Detect this case and force a layout pass.
+            if (!_presenter.IsMeasureValid)
+                (VisualRoot as ILayoutRoot)?.LayoutManager?.ExecuteInitialLayoutPass();
+
             var deltaY = _presenter.GetOffsetForPopup();
 
             // The extra 5 px I think is related to default popup placement behavior
-            _popup.Host.ConfigurePosition(_popup.PlacementTarget, PlacementMode.AnchorAndGravity, new Point(0, deltaY + 5),
-                Primitives.PopupPositioning.PopupAnchor.Bottom, Primitives.PopupPositioning.PopupGravity.Bottom,
-                 Primitives.PopupPositioning.PopupPositionerConstraintAdjustment.SlideY);
+            _popup.VerticalOffset = deltaY + 5;
         }
 
         private void OnDismissPicker(object sender, EventArgs e)

src/Avalonia.Controls/DateTimePickers/TimePickerPresenter.cs

@@ -253,6 +253,9 @@ private void OnSelectorButtonClick(object sender, RoutedEventArgs e)
 
         internal double GetOffsetForPopup()
         {
+            if (_hourSelector is null)
+                return 0;
+
             var acceptDismissButtonHeight = _acceptButton != null ? _acceptButton.Bounds.Height : 41;
             return -(MaxHeight - acceptDismissButtonHeight) / 2 - (_hourSelector.ItemHeight / 2);
         }